My Hard drive become unaccessable!?

I have 2 hard drives on my PC. the one that gone bust is an ATA for back up and other stuff i dont use alot. It was still working about 2 days ago when i played videos off it, then today when i tried to do the same thing it suddenly said 'the drive is inaccessable, ...corrupted and unreadble'. I've tried restarting, made sure plugs are in and things like that but no luck! the Hard drive is still spinning but what's wrong?

Once you got a Mac, you won't go back (apart from playing games, of course).

i tried to put a screenshot but the forum wont let coz im new!
It says the drive is not allocated. how do i allocate the drive? It just doesn't show up in the window?
it does say the drive is working properly in device management.

Once you got a Mac, you won't go back (apart from playing games, of course).